High-strength hot-dip galvanized steel sheet, high-strength alloyed hot-dip galvanized steel sheet excellent in bake hardenability, and manufacturing method thereof

A high-strength hot-dip galvanized steel sheet excellent in bake hardenability, comprising:

• a base steel sheet containing, in mass %,
• C:
• 0.075 to 0.400%,
• Si:
• 0.01 to 2.00%,
• Mn:
• 0.80 to 3.50%,
• P:
• 0.0001 to 0.100%,
• S:
• 0.0001 to 0.0100%,
• Al:
• 0.001 to 2.00%,
• N:
• 0.0001 to 0.0100%, and
• O:
• 0.0001 to 0.0100%,
• with the balance made up of Fe and inevitable impurities,
• wherein a structure of the base steel sheet contains, in volume fraction, 3% or more of a retained austenite phase, 50% or less of a ferrite phase, and 40% or more of a hard phase, at a range from 1/8 thickness centered around a 1/4 sheet thickness from a surface to 3/8 thickness centered around the 1/4 sheet thickness from the surface at the base steel sheet,
• wherein an average dislocation density is 5×1013/m2 or more,
• wherein a solid-solution C amount contained in the retained austenite phase is in mass % 0.70 to 1.00%,
• wherein an X-ray random intensity ratio of FCC iron in a texture of the retained austenite phase is 3.0 or less,
• wherein a ratio between a grain diameter relative to a rolling direction and a grain diameter relative to a sheet width direction of the retained austenite phase is 0.75 to 1.33, and
• wherein further, a hot-dip galvanized layer is formed at the surface of the base steel sheet and the sheet thickness is 0.6 to 5.0 mm.